I've been following a vague hunch about the UA shell, and Merope. Merope is a B type star. If you filter galmap for B types only, you see that there's a lot of them in the Plaiedes, and also that there's a trail of them that leads toward california nebula. You have to fiddle around to follow it, sometime shifting up and down. It starts strong, leads past Taurus dark region and up, then arches over and drops, coming on strong again up to California nebula. The nearest one to the nebula is HIP 18390 (image below courtesy of Nicholas Powell)
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There are a bunch of B types just outside the nebula, close together, similarly to the Pleides cluster of them. Using HIP 18390 or one of the nearby B's as the centre, I'd like to see if there's a UA shell around it. I know already some commanders are looking for a shell around California nebula, my hunch is that if there is, it will be pointing to one of these B types. Any help scouring if you're in the area would be great.